Methanol (methyl alcohol, wood alcohol, wood spirit, CH3OH) is widely used for industrial and automotive purposes but is unfit for consumption by humans and animals. It is common to find methanol in products like anti-freeze, canned heating sources like Sterno, varnish, windshield wiper fluid, paint thinner, and fuel additives. Poisonings occur from accidental ingestion of methanol-containing products or when it is misguidedly ingested as an ethanol substitute. A blood level of >50 mg/dl methanol is associated with severe poisoning.
Mechanism of Action
Methanol can be adsorbed through the skin or from the respiratory or gastrointestinal tract upon ingestion and is metabolized in liver. Various steps of reaction are:
- Alcohol dehydrogenase (ADH) catalyzes the conversion of methanol to formaldehyde.
- Aldehyde dehydrogenase converts formaldehyde to formic acid.
- Formic acid undergoes folate-dependent pathway (in the presence of tetrahydrofolate enzyme) and produce carbondioxide (CO2) and water.
Methanol itself has relatively low toxicity but the accumulation of formate (metabolism is very slow) in the body leads to metabolic acidosis.
Nervous system :
- CNS depression
- Prolonged coma
Late symptoms (10-30 hours after exposure)
- Visual disturbances (like being in a snow storm)
- Blurring of vision (dilation of pupils)
- Congestion of optic disc
- Severe epigastric pain
- Nausea and vomiting
- Liver damage
Other Physical Findings:
- Bluish colored lips and finger nails
- Fatigue, leg cramps, weakness
- Odor of formaldehyde in breath and urine
- Methanol concentration in blood higher than 50 mg/dl
- Metabolic acidosis with an elevated anion gap and osmolar gap
- Decrease in serum bicarbonate
Treatment and Management
There are 3 specific modalities of treatment for severe methanol poisoning:
- supression of metabolism by alcohol dehydrogenase to toxic products
- hemodialysis to enhance removal of methanol and its toxic products
- alkalinization to counteract metabolic acidosis
- Keep the patient in a quiet, dark room; protect the eyes from light
- Gastric lavage with sodium bicarbonate if the patient is brought within 2 hours of ingesting methanol. Supportive measures to maintain ventilation and BP should be instituted.
- Combat acidosis by i.v. sodium bicarbonate infusion (prevents retinal damage)
- Potassium chloride (KCl) infusion is needed only when hypokalemia occurs due to alkali therapy
- Ethanol 100 mg/dl in blood saturates alcohol dehydrogenase and retards methanol metabolism. Ethanol (10% in water) is administered through a nasogastric tube; loading dose of 0.7 ml/kg is followed by 0.15 ml/kg/hour drip.
- Nasogastric tube with activated charcoal may be inserted
- Hemodialysis (clears methanol as well as formate and hastens recovery)
- Fomepizole, an alcohol dehdrase inhibitor retards methanol metabolism. A loading dose of 15 mg/kg every 12 hours till serum methanol falls below 20 mg/dl, has been found effective and safe.
- Administration of folic or folinic acid enhances metabolism of formate
Methanol intoxication in Nepal
There was an outbreak of methanol poisoning, leading to death of 10 people in Nepal in July-August,2008. “Sofi”, a locally brewed alcoholic drink, was adulterated with methanol. It was later banned. It occured due to illiteracy and ignorance of people in rural areas and lack of proper monitoring and control by government.